1. Field of the Invention
The present invention relates to a catalyst for a polymerization of norbornene monomers, a method for producing a norbornene polymer, a method for producing a norbornene copolymer, a norbornene polymer and a transition metal complex.
2. Discussion of the Background
Conventionally, addition polymers of cyclic olefins represented by norbornene polymers have been industrially used in the field of optical films and the like as an organic material being excellent in heat resistance and transparency. There have been various reports that such addition polymers of cyclic olefins can be produced by the addition polymerization of cyclic olefin monomer(s) using a catalyst containing transition metal compounds such as Ti, Zr, Cr, Co, Ni and Pd.
For example, the European Patent Publication No. 0445755 reports that an addition homopolymer of norbornene having the number average molecular weight exceeding 1,000,000 can be produced by polymerizing a norbornene monomer alone by using a transition metal compound of elements belonging to five to ten groups of the periodic table as a main catalyst and methylaluminoxane (MAO) as a cocatalyst.
U.S. Pat. No. 3,330,815 publication discloses addition homopolymers of norbornene monomers containing polar groups and copolymers with norbornene using only dichlorobis(benzonitrile)palladium and allyl palladium chloride dimer as a catalyst.
Japanese Patent No. 3678754 (WO96/37526) and JP-A-2008-31304 publication disclose a method for improving an addition polymerization of a norbornene monomer alone containing polar group or copolymerization with norbornene. Though these methods improved both of polymerization activity and molecular weight of the obtained polymer by using a combination of allyl palladium chloride dimer, silver tetrafluoroborate and silver hexafluorophosphate as a catalyst, they only disclose copolymer having number average molecular weight less than 200,000 in examples and have not succeeded in producing copolymers having number average molecular weight of 200,000 or more which is required for mechanical properties to be developed to a practical level. In Table 1 of JP-A-2008-31304, the number average molecular weight (Mn) entries and the weight average molecular weight (Mw) entries replace each other. It is obvious from that Mw/Mn values should be around 2.5, and it is clear that a copolymer having a number average molecular weight exceeding 200,000 did not exist if data in Table 1 are interpreted properly.
International publication No. WO06/064814 (US 2009/264608) discloses that addition copolymerization of norbornene containing polar group and norbornene can be efficiently performed by using compounds of transition metals belonging to eighth to tenth groups of the periodic table as a main catalyst in combination with a cocatalyst capable of producing a cationic transition metal compound through the reaction with the main catalyst to thereby obtain copolymers having high molecular weight.
As one of the methods to prevent the catalyst deactivation due to the coordinate bonding of norbornene with a transition metal complex, it is possible to extend the distance between the polymerizable carbon-carbon double bonding and a polar group (ester group). For example, “J. Organomet. Chem., 2009, 694, p. 297-303” discloses a case of producing a homopolymer of a norbornene compound wherein a one methylene chain is introduced between the norbornene skeleton and an ester group, having a number average molecular weight of 100,000 or more, by using N-heterocyclic carbene complex.